Printing with flexographic inks and lacquer

ABSTRACT

There is described a printing unit and a method for printing with flexographic inks. The printing unit includes a screen roller engaging a doctor blade system ( 3 ), and which is in continuous operation, either by engaging a motor ( 10 ) or by operation by the transmission ( 2 ) of the printing machine. The screen roller ( 1 ) of the printing unit interacts with a rubber sheet ( 16 ) which is disposed on a rubber sheet cylinder ( 4 ) at a position between a printing plate cylinder ( 5 ) and a back-pressure cylinder ( 6 ). A slot ( 7 ) is provided in the rubber sheet, used when the screen roller ( 1 ) is to be engaged with the rubber sheet ( 17 ).

This application claims the benefit of Danish Application No. PA 200300502 filed Apr. 1, 2003 and PCT/DK2004/000230 filed Apr. 1, 2004, whichare hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

The present invention concerns a printing unit for printing withflexographic inks and lacquer in an offset printing machine thatincludes a printing plate cylinder, a rubber sheet cylinder, aback-pressure cylinder and an inking unit which includes a screen rollerin engagement with a doctor blade system and which is arranged forcontinuous rotation, either by engaging a motor in a situation where theprinting machine is not operating or by engaging the transmission of theprinting machine when the printing machine is operating, the screenroller being arranged for swinging in and out of engagement with rubbersheet cylinder which has an axially oriented channel limited by thefront edge and the rear edge of the rubber sheet.

The invention further concerns a printing machine with such a printingunit and a tool for use in mounting and dismounting the washing facilityand the inking unit in such a printing machine.

The invention furthermore concerns a method of operation for printingwith flexographic inks and lacquer in an offset printing machine whichincludes a printing plate cylinder, a rubber sheet cylinder, aback-pressure cylinder and an inking unit which includes a screen rollerengaging a doctor blade system and which is continuously rotated, eitherby engaging a motor in a situation where the printing machine is notoperating or by engaging the transmission of the printing machine whenthe printing machine is operating, the screen roller being arranged forswinging in and out of engagement with rubber sheet cylinder which hasan axially oriented channel limited by the front edge and the rear edgeof the rubber sheet

It is prior art to produce printing machines in which are placeddifferent printing units, so that an offset printing machine also can beused with flexographic inks and lacquer. Examples of such prior artmachines of the kind mentioned in the introduction are found e.g. inPCT/DK98/000303 and in EP 1 093 913.

The reason of the present invention is a need for providing a modularsystem, where a washing facility for the rubber sheet cylinder in aprinting unit readily may be substituted with an inking unit, and wherethere is no risk that ink in the screen roller of the inking unit driesup simultaneously with enabling driving the inking unit by thetransmission found in the printing machine in order to provide anoperation of the printing unit which is entirely synchronous with thenumber of revolutions of the rubber sheet.

When the printing unit is of the type with screen roller engaging adoctor blade system, problems will arise with drying of ink/lacquer inthe screen roller when the printing machine is standing still or whenthe screen roller is brought out of engagement with the rubber sheetcylinder, as the screen roller is not rotating in these situations.

When changing the printing machine by shifting between the washingfacility and the inking unit, it is important that this occurs veryquickly for reducing the down-time of the machine. By the known machinesit is furthermore an ergonomically inconvenient task to performsubstitution, since washing facilities usually are positioned obliquelyunder the rubber sheet cylinder. Therefore, it is difficult for anoperator to get a real hold on the washing facility/inking unit. Thisalso implies risk of the washing facility/printing unit falling down andcausing damage of parts in printing machine and/or the washingfacility/inking unit.

SUMMARY OF THE INVENTION

It is thus the purpose of the present invention to indicate a systemincluding a printing unit, a printing machine, a tool and a method ofthe types mentioned in the introduction that enable remedying of theproblems connected with the prior art printing units and methods.

This is achieved according to the present invention with a printing unitwhich is peculiar in that the inking unit is adapted for being mountedin the support holder of the printing machine for a washing facility forthe rubber sheet on the rubber sheet cylinder.

The printing machine according to the invention is peculiar in that ateach end of the inking unit there are projecting guide means which arearranged for interacting with at least one guide groove formed in thesupport holder of the printing machine at each end of the rollers andwhich interacts with projecting guide means on the washing facility.

The tool according to the invention for use in mounting and dismountingthe washing facility and the inking unit is peculiar in that it includestwo side plates that each are provided with positioning meansinteracting with corresponding positioning means in the support holderof the printing machine and auxiliary guide grooves that are alignedwith the guide grooves in the support holder of the printing machinewhen the positioning means engage, the guide grooves and auxiliary guidegrooves being adapted for receiving the washing facility/inking unit ata position situated under carrier handles formed at an upper side of thetool, preferably on the side plates, and which is used for lifting whenmounting and dismounting the washing facility and the inking unit.

The method according to the invention is peculiar in that the inkingunit is displaced in the support holder for a washing facility for therubber sheet on the rubber sheet cylinder for mounting and dismounting,respectively, when substituting with the washing facility.

As the inking unit is modular and can be displaced in the support holderof the printing machine, a rapid and easy change of the printing machineis achieved for mounting or dismounting the washing facility and theinking unit, respectively. This may occur particularly rapidly andsimply by using the tool according to the invention.

The screen roller in the inking unit will rotate continuously. Duringusual operation of the printing unit, where it is essential that thescreen roller is running synchronously with the rubber sheet, rotationis established by engagement with the transmission of the printingmachine. This may e.g. occur via a driving gear wheel located at aninternal side of the side frame of the printing unit and engaging thedriving gear wheel on the inking unit shaft on which the screen rolleris mounted. Hereby is achieved a 100% accurately synchronisedtransmission that ensures correct speed between the rubber sheetcylinder of the printing machine and the screen roller of the inkingunit. As opposed to using an independent drive motor, e.g. servomotorfor driving the inking unit, there will be no tolerance problems withregard to number of revolutions of rubber sheet and screen roller,respectively.

In order to ensure continuous rotation when the screen roller is swungout from its engagement with the rubber sheet, a motor running withconstant rotational speed has been provided. This motor can drive thescreen roller independently of the operation of the printing machine.The motor is permanently integrated in the inking unit of the printingmachine (offset printing unit) and is therefore not to be installed eachtime the inking unit is to be used. The used principle is also calledidling for the inking unit. Furthermore, the inking unit will requireless maintenance than an inking unit driven by an independent driveunit, e.g. a servomotor.

The printing unit according to the invention is primarily intended foruse with printing machines that are adapted to printing on sheets. Byusing the inking unit, the printing unit is changed from an offsetprinting unit to a lacquering unit/flexographic unit, where lacquer/inkfrom the screen roller is deposited on the rubber sheet in a waycorresponding to a cliché in flexographic printing. The print is thenpassed further down onto the sheet. The inking unit of the printing unitis structured as a modular arrangement that may be placed ingrooves/fittings used for the printing unit washing facility for therubber sheet

Rapid shifting between washing facility and inking unit is possible withthe tool according to the invention. The grooves of the tool furthermoreprovide secure guiding of washing facility as well as inking unit sothat there is no risk of damaging parts of the unit while making thechange.

According to a particular embodiment, the printing unit is peculiar inthat the screen roller is arranged for swinging against the rubber sheetcylinder opposite the duct in order to be in contact with the rubbersheet from its front edge. The screen roller will be arranged forswinging away from the rubber sheet cylinder opposite the channel inorder to be in contact with the rubber sheet to its rear edge. Inpractice, the swinging is performed when the penultimate sheet in aprinting series is inserted in the printing unit.

Before the printing unit is put into use, it is important that there isspacing between the rubber sheet and the printing plate cylinder.According to one embodiment, this occurs in practice by dismounting thepressure plate, as lacquer can otherwise be deposited on the printingplate with consequent risk that the lacquer is passed further up intothe printing unit. Furthermore, it is noted that the moistening unit ofthe printing machine is to be disconnected.

No offset ink is to come on the rubber sheet where the printing unit isused for printing. Therefore, it is important to have the entire sheetlacquered from the front edge since the rubber sheet and printing resultotherwise can be destroyed. If there is no lacquer on the rubber sheet,the offset ink is drawn from the sheet up on the rubber sheet.

For ensuring that a first sheet moved through the printing machine isfully lacquered, it is important that the printing unit is printing fromthe front edge of the first sheet and not at an earlier time. This isensured by establishing the screen roller engagement opposite to theaxially oriented channel. At commencing pressure, the screen roller ofthe printing unit is thus moved in against the rubber sheet cylinder ina position from the axially oriented channel in the rubber sheetcylinder. Therefore, contact with the rubber sheet will be establishedfrom its front edge. If there is lacquer on the rubber sheet at anearlier time than the time where a first sheet is inserted into theprinting unit, the lacquer will be transferred from the rubber sheetcylinder to the back-pressure cylinder, which is not acceptable.

As mentioned, the sheet is to be provided with lacquer across its entirelength, and therefore it is important that the screen roller can be incontact with the rubber sheet for applying lacquer to the rear edge ofthe rubber sheet. When at a position opposite the channel beyond therear edge, it is possible to swing out the screen roller.

It is important that the last sheet in a print series coming through theprinting unit is lacquered completely. However, the screen roller willusually be swung back from the rubber sheet before the sheet has enteredthe printing unit. Thereby it is ensured that the rubber sheet is notfilled with lacquer at the end of a printing process. In practice, thisoccurs by the screen roller being swung out before the last sheet in aseries of print being inserted in contact with the rubber sheet.

According to a further embodiment, the printing unit is peculiar in thatinteracting bearing means on the inking unit and the printing machineare provided for adjusting the contact pressure of the inking unitagainst the rubber sheet. Hereby is ensured correct contact pressure foroptimising ink deposition during printing and possibility forcompensating for difference in mutual position of the cylinders, e.g. asa consequence of different thickness on the sheets.

DESCRIPTION OF DRAWING

The invention will now be explained more closely with reference to theaccompanying drawing, where:

FIG. 1 shows a schematic view of the elements forming part of a printingunit according to the invention;

FIG. 2 illustrates different steps by a method according to theinvention;

FIG. 3 shows a schematic view of support holders in a printing machineaccording to the invention with mounted inking unit;

FIG. 4-5 show schematic views of support holders in a printing machineaccording to the invention that interact with side plates in a toolaccording to the invention with the inking unit during dismounting;

FIG. 6 shows a schematic partial view of guiding means on a side plateof the printing unit;

FIG. 7 shows a schematic side view of the parts shown in FIG. 6 andfurthermore showing the drive connection for the screen roller; and

FIG. 8 shows a schematic view of a tool according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 is shown an inking unit T that includes a screen roller 1rotating in direction of the indicated arrow. The screen roller 1engages the transmission of the printing machine as indicated by a gearwheel 2. The screen roller can also be driven by a motor 10 for idlingof the screen roller.

The screen roller 1 engages a doctor blade system 3 forming part of theinking unit T and which is mounted at a position over a drip pan 11 withthe possibility of displacing the screen roller 1 out from and intowards a rubber sheet cylinder 4. In practice this occurs by contactbetween screen roller and the doctor blade system being maintained andthat displacement occurs by swinging the inking unit T. This occursabout an axis guiding the gear wheel 33 of the screen roller (see FIG.7) through a swinging movement about the gear wheel 2, yet withengagement maintained.

In practice, the motor 10 will have a gear wheel 39 (see FIG. 7) whichis in constant engagement with the gear wheels of the printing machine 2that are engaged or disengage from the drive system of the main machineby using a coupling (not shown) which is activated synchronously withthe swinging in and out of the screen roller. The gear wheel 39 isconnected with the motor 10 via an idling so that the motor is notdriven with when the screen roller 1 is driven by the printing machine.

The rubber sheet cylinder 4 engages a pressing plate cylinder 5 and aback-pressure cylinder 6. A rubber sheet 14 is placed on the rubbersheet cylinder 4 with a channel 7 which is delimited by a front edge 12and a rear edge 13 of the rubber sheet 14. In FIG. 1 is indicated that aslot 8 can be provided between the rubber sheet 14 and the pressingplate cylinder 5. Furthermore, in FIG. 1 is indicated a sheet 9 which ison its way into the printing unit. The cylinders of the printing unitare rotated in the direction indicated by the arrows.

In FIG. 2 are shown different Figures that illustrate different steps ofthe method.

In the first step A, the printing machine is started and is runningstandby. In this position, the inking unit T will run in idling byengaging the motor 10.

In the second step B, the printing machine will be set to run idling andis then ready for printing. In this position, the inking unit T willstill run in idling which is now occurring by using/coupling in thetransmission 2 of the printing machine (not shown curring byusing/coupling in the transmission 2 of the printing machine (not shownin FIG. 2).

In the third step C, signal for starting printing in the printingmachine is given. At this time, the inking unit will continue to run inidling with the transmission of the printing machine and simultaneouslythe first sheet is fed into the printing unit. Ink will be applied tothe sheet in the printing units (not shown) of the printing machinelocated at an upstream position in the printing machine.

In the fourth step D, the printing machine will give signal foractivation of the printing unit, and the channel 7 in the rubber sheet14 will be situated at a position opposite the printing plate cylinder5. The printing unit will now await correct positioning of the channel 7of the rubber sheet cylinder before swinging in. The first sheet 9 inthe system is now on its way into the printing unit according to theinvention, and it will be provided with colour print from previousprinting units.

In the fifth step E, the printing unit will still be activated, and thechannel 7 in the rubber sheet cylinder will now be on its way to aposition opposite the screen roller 1 in the inking unit T according tothe invention. Now there will given a starting signal to the printingunit which starts its swinging in movement at the same time as the firstsheet is on its way into the printing unit.

In the sixth step F, there is still a signal for activating the printingunit, and the channel 7 in the rubber sheet cylinder will now besituated opposite to the screen roller 1 of the printing unit. Thescreen roller is brought in against the channel for being in engagementwith the rubber sheet 14 from its front edge. From now on, lacquer isapplied to the rubber sheet. The sheet 9 will now be with its front edgeat a position immediately in front of the back-pressure cylinder 6.

In the seventh step G, the printing unit is activated, and the screenroller 1 transfers lacquer/flexographic ink to the rubber sheet 14. Thecontact pressure against the rubber sheet is adjusted by usinginteracting bearing means on the inking unit and the printing machine.The sheet 9 will now be provided with lacquer from the front edge of thesheet until it leaves the printing unit.

When the sheet has left the printing unit, the succeeding sheet willcome in direct continuation of the first sheet where the screen rollerremains in engagement until a time before the last sheet in a printseries is inserted on the rubber sheet.

In the eighth step H is shown a situation where the last sheet 9′ in aprint series is on its way into the printing unit. Here, the screenroller 1 is swung away from the rubber sheet, which has occured when itwas opposite the channel 7 at the insertion of the last sheet 9′ in aprint series in the printing unit. Thus no lacquer/flexographic ink areapplied to the rubber sheet during the passage of the last sheet throughthe printing unit.

FIG. 3 shows an inking unit T mounted with the screen roller 1 engagingthe rubber sheet roller (not visible in FIG. 3). It is noted that thedoctor blade system 3 is, not mounted in the inking unit in FIG. 3. Theprinting machine includes side support holders 15 which are providedwith grooves 16 that interact with guide means in the form of pins 17 onside plates 18 in the inking unit T.

The side plates 18 are provided with a locking means 19 that enablesecuring of the inking unit T in the engaging position. The lockingmeans 19 interact with side support holder 15 and may be swung to a freeposition as illustrated in FIGS. 4 and 5.

The groove 16 has a first part 20 ending in a first downwards directedhollow 21 in which a guide pin 17 can rest at commencing release of theinking unit. This enables dismounting and mounting the inking unit aswell as washing facility in a secure and controlled way without any riskof damaging parts of the machine at mounting/dismounting. When thewashing facility is moved to its first rest position, it will assume aposition as illustrated in FIG. 5.

FIG. 3 furthermore shows a bearing means 41 in the shape of a surface atthe top side of the side plate 18 of the printing unit. This bearingmeans interacts with a bearing means 42 on the printing machine. Thebearing means 42 is provided in the shape of a spindle 43 which isactuated by a worm situated in a housing 44. The worm can be connectedwith a transverse rod connection in order to activate a correspondingworm drive and adjusting spindle at the opposite side of the printingunit. By extending the piston 43 more or less from the housing 44, itbecomes possible to press on the side plate 18, whereby the inking unitis imparted a swinging movement that moves it closer to the rubber sheetcylinder or farther from the rubber sheet cylinder, whereby the bearingpressure is adjusted.

According to a particular embodiment, it is possible to incorporate ameter, e.g. a potmeter, in the worm housing 44. This may be combinedwith a meter measuring the position of the rubber sheet which also canbe provided by means of a potmeter. Hereby, it becomes possible to givea signal from a control unit so that secure knowledge of the mutualposition of the rubber sheet 14 and the screen roller 1 is obtained. Thebearing pressure may hereby be adjusted, e.g. with regard to varyingpaper thicknesses.

In FIG. 4 is illustrated a tool 22 according to the invention. The tool22 is provided with side plates 23 resting on each their support holder15 in the printing machine. The side plates 23 are provided withpositioning means 24 in the form of a pin that interact with positioningmeans in the shape of a groove 25 in the support holder 15 of theprinting machine. Further positioning occurs by interaction between aninteracting part 26 on the side plate 23 which interacts with a groove27 in the support holder 15. When the side plate is mounted correctly, afirst auxiliary groove 28 in the side plate will be aligned with thegroove 16. Via an adjustable closing plate 30, a further auxiliarygroove 29 in the side plate 23 will be in contact with the upper side ofthe support holder 15. Hereby it is possible that a second guide pin 17′(see FIG. 6), which is placed in the side plate 18 of the inking unit,is brought to engaging the further auxiliary groove 29, while the firstguide pin 17 after passing the groove 16 is brought into engaging theauxiliary groove 28 in the tool 22.

When the inking unit T is disposed in the auxiliary guide grooves 28,29, the plate 30 is swung upwards to a locking position as illustratedin FIG. 8. The inking unit, or alternatively the washing facility, willhereby be placed in the auxiliary guide groove in a position situatedunder carrier handles 31 disposed at the upper side of the tool 22. Thecarrier handles 31 are formed as handles on a through-going rod 32passing through the side plates 22. The auxiliary tool enables for oneperson at each end of the printing machine to mount and dismount washingfacility/inking unit without any ergonomically disadvantageous workingpositions. In practice it has furthermore appeared thatmounting/dismounting by means of the tool reduces the shifting time toone-fifth of the shifting time without using auxiliary tool.Furthermore, use of the tool 22 provides a complete controlling of theway in which mounting and dismounting occurs, so that the washingfacility/inking unit never come in inadvertent contact with the printingmachine with consequent risk of damaging machine parts.

In FIG. 4 is seen that the lock 19 is swung into an open positionwhereby the first guide pin 17 can pass into the first part 20 of thegroove 16.

In FIG. 5, the first part of the dismounting movement is shown, wherethe inking unit is situated with the guide pin 17 in the restingposition 21 at the bottom of the first part 20 of the groove 16. In thisposition, a slightly outwards pull in the inking unit will cause thatthe second guide pin 17′ is moved beyond the support holder and theplate 30, into the further auxiliary groove 29 simultaneously with thefirst guide pin 17 being moved through the groove 16 to placing at thebottom of the auxiliary guide groove 28 in the side plate 23 of thetool.

FIG. 6 illustrates schematically the positioning of the guide pins 17,17′ projecting from the side plate 18 in the inking unit. Furthermore,FIG. 6 illustrates a gear wheel 33 which is mounted on the axle 34supporting the screen roller 1. The gear wheel 33 is situated at anoutwards facing position of the side plate 18. The gear wheel 33 engagesthe gear wheel 2 for the transmission of the printing machine. Via ashaft 40 passing through the lateral flange 35 of the printing machine,the gear wheel 2 engages a drive gear wheel 36 connected to the driveunit of the main machine. The connection between gear wheels 36 and 32is established by means of a coupling 37 that enable disengagement ofthe gear wheel 2 from the engagement with the gear wheel 36. Byactivating/deactivating the coupling 37, one may freely choose whetherthe gear wheel 2 is to be freely rotating or driven by the main driveunit via the engagement with the gear wheel 36.

When the gear wheel 2 is rotating freely, idling can be established byactivating a motor 38 which via the gear wheel 39 drives the gear wheel2 and thereby the screen roller 1. The continuous rotation of the screenroller 1 is hereby established, irrespectively whether the printingmachine is operating or not

In FIG. 8 is seen that the tool 22 includes two side plates 23 that aremutually connected via the rod 32. In the internal side of each sideplate there is provided auxiliary guide grooves 28, 29 so that thewashing facility/inking unit can be received at a position located underthe carrier handles 31. The tool 22 may thereby be used for lifting thewashing facility/inking unit by mounting and dismounting.

It is noted that the above embodiment is just a concrete embodiment fora system according to the invention. Other embodiments will also bepossible within the scope of the subsequent claims. The drivearrangement may thus be provided with other means than gear wheels, e.g.friction wheels or toothed belts. Furthermore, guide pins and guidegrooves may be mutually exchanged so that guide pins are situated on thesupport holder of the printing machine instead of the inkingunit/washing facility. Furthermore, guide grooves may have otherembodiments than the shown embodiments, if only it is ensured thatdismounting and mounting occurs without interference between machineparts.

1. Printing unit for printing with flexographic inks and lacquer in anoffset printing machine that includes a printing plate cylinder, arubber sheet cylinder, a back-pressure cylinder and an inking unit whichincludes a screen roller in engagement with a doctor blade system andwhich is arranged for continuous rotation by engaging a motor in asituation where the printing machine is not operating and by engaging atransmission of the printing machine when the printing machine isoperating, the screen roller being arranged for swinging in and out ofengagement with the rubber sheet cylinder which has an axially orientedchannel limited by a front edge and a rear edge of a rubber sheet,wherein the inking unit is adapted for being mounted in a support holderof the printing machine for a washing facility for the rubber sheet onthe rubber sheet cylinder.
 2. Printing unit according to claim 1 and foran offset printing machine adapted for printing sheets, characterized inthat the screen roller is arranged for swinging against the rubber sheetcylinder opposite the duct in order to be in contact with the rubbersheet from its front edge.
 3. Printing unit according to claim 2,characterized in that the screen roller is arranged for swinging awayfrom the rubber sheet cylinder opposite the channel in order to be incontact with the rubber sheet to its rear edge.
 4. Printing unitaccording to claim 1, characterized in that interacting bearing means onthe inking unit and the printing machine are provided for adjusting thecontact pressure of the inking unit against the rubber sheet. 5.Printing machine with a printing unit according to claim 1,characterized in that at each end of the inking unit there areprojecting guide means which are arranged for interacting with at leastone guide groove formed in the support holder of the printing machine ateach end of the rollers and which interacts with projecting guide meanson the washing facility.
 6. Tool for use in mounting and dismounting thewashing facility and the inking unit in a printing machine according toclaim 5, characterized in that it includes two side plates that each areprovided with positioning means interacting with correspondingpositioning means in the support holder of the printing machine andauxiliary guide grooves that are aligned with the guide grooves in thesupport holder of the printing machine when the positioning meansengage, the guide grooves and auxiliary guide grooves being adapted forreceiving the washing facility/inking unit at a position situated undercarrier handles formed at an upper side of the tool, preferably on theside plates, and which is used for lifting when mounting and dismountingthe washing facility and the inking unit.
 7. Method of operation forprinting with flexographic inks and lacquer in an offset printingmachine which includes a printing plate cylinder, a rubber sheetcylinder, a back-pressure cylinder and an inking unit which includes ascreen roller engaging a doctor blade system and which is continuouslyrotated by engaging a motor in a situation where the printing machine isnot operating and by engaging a transmission of the printing machinewhen the printing machine is operating, the screen roller being arrangedfor swinging in and out of engagement with the rubber sheet cylinderwhich has an axially oriented channel limited by a front edge and a rearedge of a rubber sheet, wherein the inking unit is displaced in asupport holder of the printing machine for a washing facility for therubber sheet on the rubber sheet cylinder for mounting and dismounting,respectively, by substituting with the washing facility.
 8. Methodaccording to claim 7 and for offset printing on sheets, characterized inthat the screen roller is swung in and out of engagement with the rubbersheet cylinder, as it is brought in contact with the rubber sheet fromits front edge simultaneously with a first sheet in a series of printsis inserted in the printing unit.
 9. Method according to claim 7,characterized in that the screen roller is swung against the rubbersheet cylinder opposite the channel in order to be in contact with therubber sheet from its front edge.
 10. Method according to claim 8,characterized in that the screen roller is swung away from the rubbersheet cylinder opposite the channel at the penultimate sheet in aprinting series in order to be in contact with the rubber sheet at itsrear edge.